High solids coating composition adapted for use as automotive topcoat-#3

ABSTRACT

A fast curing, high solids coating composition adapted for use as an automotive topcoat, which upon curing forms a hard, glossy, durable coating exhibiting excellent resistance to solvents and water. The coating composition contains greater than about 60 percent by weight of non-volatile solids and, exclusive of pigments, solvents and other nonreactive components, consists essentially of: 
     (A) a copolymer bearing pendant epoxy functionality, having a number average molecular weight (M n ) of between about 1500 and about 10,000 and a glass transition temperature (Tg) of between about -25° and about 70° C.; 
     (B) a reactive catalyst comprising at least one hydroxy functional organophosphate ester selected from certain mono- and diesters of phosphoric acid; 
     (C) an amine-aldehyde crosslinking agent; and 
     (D) optionally, a hydroxy functional additive. 
     The hydroxy functional organophosphate ester is included in the composition in an amount sufficient to provide between about 0.67 and about 1.4 equivalents of acid functionality for each equivalent of pendant epoxy functionality of copolymer (A), and the amino crosslinking agent is included in the composition in an amount sufficient to provide at least about 0.4 equivalents of nitrogen crosslinking functionality for each equivalent of hydroxy functionality included in the composition.

This application is a continuation-in-part of Ser. No. 864,960 filedDec. 27, 1977, and now abandoned.

BACKGROUND OF THE INVENTION

This invention is related to a fast curing, high solids, thermosettingcoating composition. More particularly, the invention relates to apolymeric, high solids, fast curing coating composition adapted toprovide an automotive topcoat which demonstrates hardness, high gloss,outstanding durability and excellent resistance to solvents and water.Still more particularly, this invention relates to a fast curing, highsolids, thermosetting ocating composition adapted to be used as anautomotive topcoat wherein the topcoat includes metallic flake as apigment.

Because of increasingly strict solvent emissions regulations in recentyears, low solvent emission paints have become very desirable. A numberof high solids paint compositions have been proposed to meet these lowsolvent emission requirements. However, many of these compositions aredeficient because of difficulty in application, slow curing rates, lackof flexibility, poor durability and low solvent and water resistance.Many of the proposed compositions have been particularly deficient asautomotive topcoats, particularly when the topcoat is to includemetallic flake as a pigment.

The deficiency in compositions including metallic flake results fromundesired reorientation of the metallic flake during application andcure of the coating. Flake reorientation results primarily because ofthe very low viscosity resins used in the paint compositions toaccommodate high solids. The low viscosity is not sufficient toimmobilize the flakes which tend to redistribute themselves to show"reverse flop" and nonuniform distribution.

The coating compositions of this invention combine the above discusseddesired properties and low application viscosity with rapid cure so asto overcome deficiencies of previously proposed high solids materialsand thereby achieve a high solids coating composition particularlyadapted for automotive topcoats and still more particularly adapted forautomotive topcoats including metallic flake as a pigment.

SUMMARY OF THE INVENTION

The thermosetting coating composition of this invention contains greaterthan about 60 percent by weight of nonvolatile solids, preferablygreater than about 70 percent by weight, and is capable of curingrapidly at a low temperature. The composition, exclusive of pigments,solvents and other nonreactive components, consists essentially of:

(A) a copolymer bearing pendant epoxy functionality, having a numberaverage molecular weight (M_(n)) of between about 1500 and about 10,000,preferably between about 2,000 and about 6,000, and a glass transitiontemperature (Tg) of between about -25° C. and about 70° C., preferablybetween about -10° C. and about 50° C., the copolymer consisting ofbetween about 10 and about 30 weight percent of monoethylenicallyunsaturated monomers bearing glycidyl functionality and between about 90and about 70 weight percent of other monoethylenically unsaturatedmonomers;

(B) a reactive catalyst comprising at least one hydroxy functionalorganophosphate ester having the formula: ##STR1## wherein n=1 to 2 andR is selected from the group consisting of mono- or dihydroxy alkyl,cycloalkyl, or aryl radicals;

(C) an amine-aldehyde crosslinking agent; and

(D) up to about 45 weight percent based on the total weight of (A), (B),(C) and (D) of a hydroxy functional additive having a number averagemolecular weight (M_(n)) of between about 150 and about 6,000.

The organophosphate ester is included in the composition in an amountsufficient to provide between about 0.67 and about 1.4 equivalents,preferably between about 0.8 and about 1 equivalents, of acidfunctionality for each equivalent of pendant epoxy functionality of thecopolymer. The amino resin crosslinking agent is included in thecomposition in an amount sufficient to provide at least about 0.4equivalents, preferably between about 0.6 and about 2.1 equivalents, ofnitrogen crosslinking functionality for each equivalent of hydroxyfunctionality included in the composition either as (i) an organichydroxyl group on the organophosphate ester, (ii) a hydroxyl group onthe optional hydroxy functional additive or (iii) as a result ofesterification of the pendant epoxy functionality of the copolymer of(A) during cure of the coating composition. In addition, the high solidscoating composition of the invention may include additives such ascatalysts, antioxidants, U.V. absorbers, flow control or wetting agents,antistatic agents, pigments, plasticizers, solvents, etc.

PRIOR ART

U.S. Pat. Nos. 3,960,979 and 4,018,848 to Khanna teach high solidscoating compositions adapted for use as a can coating material. Thecompositions consist essentially of (i) aromatic epoxide compositionshaving two or more epoxy groups on an epoxy resin which has a molecularweight not exceeding 2500; (ii) an amino crosslinking agent; (iii) aninorganic or organic monomeric or polymeric acid which acts as areactive catalyst; and (iv) a flexiblizing polyol.

The compositions of Khanna have the advantage of quick reaction and lowapplication viscosity, but lack durability, and, therefore, do notweather well. This is, in part, because of the presence of etherlinkages in the aromatic epoxides. As such, the compositions of Khannaare not desirable for use as automotive topcoats. The Khanna patentsdescribe the compositions as a low cure system. However, whenconsidering the specific teachings of the patents one finds that thecomposition includes an excess of epoxide resin, apparently with thepurpose of "killing off" excess catalyst after completion of the curingreaction. Excess epoxy resin in the composition remains uncured at thelow temperature bake range of the baking temperatures disclosed, notgiving a complete cure and desirable hardness, durability or solventresistance. If heated to higher temperatures, as called for in theexamples, the excess epoxy does react with excess hydroxy functionalityto give still further ether linkages. These ether linkages so obtainedhave a further deleterious effect on durability and make the materialsparticularly unsuitable for use as an automotive topcoat. Also, thenecessary high bake temperatures to achieve the utilization of thisexcess epoxy makes the composition undesirable from an energy point ofview. Still further, because the epoxy/catalyst reaction occurs inearlfy stages of the cure, thus "killing off" the catalyst, themelamine-hydroxy curing reaction must proceed substantially withoutbenefit of catalysis. The curing reaction thus proceeds slowly andrequires the higher temperatures of the Khanna examples.

DETAILED DESCRIPTION OF THE INVENTION

The high solids coating compositions of this invention overcomedisadvantages of prior art high solids compositions, including those ofKhanna, to provide a system which is particularly suitable for thoseapplications requiring high gloss, hardness, durability, and highsolvent and water resistance as well as a fast cure rate at lowtemperatures, e.g., between about 75° C. and about 150° C., preferablybetween about 110° C. and about 130° C. The desirable characteristics ofthe coating compositions of this invention result from the carefullycontrolled admixture of the particular components, including a hydroxyfunctional organophosphate ester, to achieve substantially completeutilization of reactant functionality and a resultant highly crosslinkedcoating in a fast and efficient manner.

Each of the components of the high solids coating compositions, theamounts of each of the components required to achieve the desiredresults of the invention and a method for applying the composition aredescribed hereinafter in greater detail.

EPOXY FUNCTIONAL COPOLYMER

A principal material in the high solids coating compositions of thisinvention is an epoxy functional copolymer bearing pendant epoxyfunctionality, and which may be prepared by conventional free radicalinduced polymerization of suitable unsaturated monomers. The term"copolymer" as used herein means a copolymer of two or more differentmonomers.

The copolymers used in the high solids coating compositions of thisinvention have a number average molecular weight (M_(n)) of betweenabout 1500 and about 10,000, preferably between about 2,000 and about6,000, and a glass transition temperature (Tg) of between about -25° C.and about 70° C., preferably between about -10° C. and about 50° C. Themonomers used to prepare the copolymer include between about 10 andabout 30 weight percent of one or more monoethylenically unsaturatedmonomers bearing glycidyl functionality. These monoethylenicallyunsaturated monomers may be glycidyl ethers or glycidyl esters.Preferably, however, the epoxy functional monomers are glycidyl estersof monoethylenically unsaturated carboxylic acids, e.g., glycidylacrylate or glycidyl methacrylate. These monomers provide the copolymerwith its pendant epoxy functionality.

The remainder of the monomers forming the epoxy functional copolymer,i.e., between about 90 and about 70 weight percent of the monomers ofthe copolymer, are other monoethylenically unsaturated monomers. Thesemonoethylenically unsaturated monomers are preferably alpha-betaolefinically unsaturated monomers, i.e., monomers bearing olefinicunsaturation between the two carbon atoms in the alpha and betapositions with respect to the terminus of an aliphatic carbon-to-carbonchain.

Among the alpha-beta olefinically unsaturated monomers which may beemployed are acrylates (meaning esters of either acrylic or methacrylicacids) as well as mixtures of acrylates and vinyl hydrocarbons.Preferably, in excess of 50 weight percent of the total of the copolymermonomers are esters of C₁ -C₁₂ monohydric alcohols and acrylic ormethacrylic acids, e.g., methylmethacrylate, ethylacrylate,butylacrylate, butylmethacrylate, hexylacrylate, 2-ethylhexylacrylate,laurylmethacrylate, etc. Among the monovinyl hydrocarbons suitable foruse in forming the copolymers are those containing 8 to 12 carbon atomsand including styrene, alpha-methylstyrene, vinyl toluene,t-butylstyrene and chlorostyrene. When such monovinyl hydrocarbons areemployed, they should constitute less than 50 weight percent of thecopolymer. Other monomers such as vinyl chloride, acrylonitrile,methacrylonitrile, and vinyl acetate may be included in the copolymer asmodifying monomers. However, when employed, these modifying monomersshould constitute only between about 0 and about 30 weight percent ofthe monomers in the copolymer.

In preparing the epoxy functional copolymer, the epoxy functionalmonomers and the remaining monoethylenically unsaturated monomers aremixed and reacted by conventional free radical initiated polymerizationin such proportions as to obtain the copolymer desired. A large numberof free radical initiators are known to the art and are suitable for thepurpose. These include: benzoyl peroxide; lauryl peroxide;t-butylhydroxy peroxide; acetylcyclohexyl; sulfonyl peroxide;diisobutyryl peroxide; di-(2-ethylhexyl) peroxydicarbonate;diisopropylperoxydicarbonate; t-butylperoxypivalate; decanoyl peroxide,azobis(2-methylpropionitrile), etc. The polymerization is preferablycarried out in solution using a solvent in which the epoxy functionalcopolymer is soluble. Included among the suitable solvents are toluene,xylene, dioxane, butanone, etc. If the epoxy functional copolymer isprepared in solution, the solid copolymer can be precipitated by pouringthe solution at a slow rate into a nonsolvent for the copolymer such ashexane, octane, or water under suitable agitation conditions.

The pendant epoxy functional copolymer useful in the compositions ofthis invention can also be prepared by emulsion polymerization,suspension polymerization, bulk polymerization, or combinations thereof,or still other suitable methods. In these methods of preparingcopolymers, chain transfer agents may be required to control themolecular weight of the copolymer to a desired range. When chaintransfer agents are used, care must be taken so they do not descreasethe shelf stability of the composition by causing premature chemicalreactions.

ORGANOPHOSPHATE ESTER

A second essential component of the high solids coatings of thisinvention is a reactive catalyst which comprises a novel hydroxyfunctional organophosphate which is present in the composition as amono- or diester or as a mixture of such mono- and diesters. The hydroxyfunctional organophosphate esters useful in the composition of theinvention are those having the formula: ##STR2## wherein n=1 to 2 and Ris selected from the group consisting of mono- or dihydroxy alkyl,cycloalkyl, or aryl radicals. Preferably, the hydroxy bearing alkyl,cycloalkyl, or aryl radicals contain 3 to 10 carbon atoms.

Among the numerous suitable mono- or dihydroxy functional radicals are:2-ethyl-3-hydroxyhexyl; 4-methylol-cyclohexylmethyl; 2,2diethyl-3-hydroxypropyl; 8-hydroxyoctyl; 6-hydroxyhexyl;2,2-dimethyl-3-hydroxypropyl; 2-ethyl-2-methyl-3-hydroxypropyl;7-hydroxyheptyl; 5-hydroxypentyl; 4-methylolbenzyl; 3-hydroxyphenyl; 2,3dihydroxypropyl; 5,6 dihydroxyhexyl; 2-(3-hydroxycyclohexyl)-2-hydroxyethyl; and 2-(3-hydroxypentyl)-2-hydroxyethyl.

The above radicals are intended to be only exemplary and numerous otherradicals falling within the defined scope of the novel organophosphateesters useful in the compositions of the invention will be apparent tothose skilled in the art. Among the most preferred radicals are mono- ordihydroxy functional alkyl radicals containing 3 to 10 carbon atoms.

A preferred method for preparing the hydroxy functional organophosphateesters useful in the compositions of the invention is by anesterification reaction between an excess of an alkyl, cycloalkyl oraryl diol or triol and phosphorus pentoxide. When a triol is used as areactant, preferably at least one of the hydroxyl groups should besecondary. The reaction between the diol or triol and the phosphoruspentoxide is generally carried out by adding phosphorus pentoxideportionwise to an excess of diol or triol in a liquid state or insolution in a suitable solvent.

Suitable solvents include, but are not limited to, butyl acetate, methylethyl ketone, methyl amyl ketone, toluene, xylene, etc.

A preferred temperature for carrying out the reaction is between about50° C. and about 60° C. Due to the multiple hydroxy functionality of thediol or triol reactant, minor amounts of polymeric acid phosphate aswell as certain cyclophosphates are also generated during the synthesis.These polymeric and cyclic materials also serve as a reactive catalystand, therefore, need not be separated from the hydroxyphosphate estersdescribed above. In fact, it has been found advantageous in preferredembodiments of the invention to employ all reaction products, i.e., thehydroxy functional organophosphate esters and the minor amount ofpolymeric acid phosphate cyclophosphates, as well as excess diol ortriol in the coating compositions. The excess diol or triol serves inthose compositions as the optional hydroxy functional additive. Reactivecatalysts prepared by the above preferred method will generally includeabout a 1 to 1 ratio of the mono- and diester organophosphate.

Still another preferred method of preparing the hydroxy functionalorganophosphate esters useful in compositions of the invention is by anesterification reaction between phosphoric acid and an alkyl, cycloalkylor arylmonoepoxide. This reaction is carried out by adding between about1 and about 2 moles, preferably between about 1 and about 1.5 moles, ofthe monoepoxy material to 1 mole of phosphoric acid or its solution in asuitable solvent as above. During the esterification reaction whichoccurs, a hydroxyl group is formed. If a dihydroxy radical is desired inthe organophosphate ester, a monoepoxide bearing hydroxy functionalitymay be used as a reactant. Preferred monoepoxide materials useful inthis method are well known monoepoxides selected from monoepoxy ethers,monoepoxy esters and alkylene oxides. Exemplary of preferredmonoepoxides for use in this esterification reaction are: propyleneoxide, butylene oxide, cyclohexene oxide, styrene oxide, n-butylglycidylether, ethylglycidyl ether, n-butylepoxy stearate and glycidyl acetate.As will be understood by those skilled in the art, the proportion ofmonoester and diester formed by the reaction will vary with the selectedmolar ratio of the monoepoxide and the phosphoric acid. When 1 mole ofmonoepoxide is used per mole of phosphoric acid primarily monoester isformed while a molar ratio of 2 to 1 results in primarily diester. Amolar ratio of 1.5 to 1 will result in an approximately 1 to 1 mixtureof mono- and diesters. In all cases a minor amount of the triester willbe formed. While this triester obviously will not serve as a reactivecatalyst, it will crosslink with the amino crosslinking agent of thecomposition and, thus, may be safely included.

The hydroxy functional organophosphate ester component of the highsolids coating composition of the invention is a reactive catalyst whichallows the composition to cure rapidly at a low temperature. The acidfunctionality of the mono- or diester or mixture of such esters reactswith the pendant epoxy functionality of the epoxy functional copolymerto form an ester and a hydroxyl group. This hydroxyl group, as well asthe organic hydroxyl groups on the hydroxy functional organophosphateester and any optional hydroxy groups included in the composition in theform of hydroxy functional additive, including any diol or triol presentfrom the synthesis of the hydroxy functional organophosphate ester,crosslinks with the amino resin crosslinking agent. It is critical toachieving the desired results of the high solids coating compositions ofthis invention, i.e., in making them suitable for use as automotivetopcoats, that the amount of organophosphate ester be sufficient toconvert substantially all of the epoxy functionality on the copolymer tothe desired hydroxy functionality by esterification reaction. Therefore,the organophosphate ester is included in the composition in an amountsufficient to provide between about 0.67 and about 1.4 equivalents,preferably between about 0.8 and about 1 equivalents, of acidfunctionality for each equivalent of pendant epoxy functionality on thecopolymer. As will be noted from the equivalent amounts of epoxy andorganophosphate ester acid functionality stated above, the amount ofacid functionality need not be in stoichiometric amounts to the epoxyfunctionality. This is because of the fact that during curing of thehigh solids coating composition, residual water present in thecomposition hydrolyzes some of the esterified product back to acid andthis hydrolyzed product then, in turn, reacts with additional epoxyfunctionality.

AMINO CROSSLINKING AGENT

A third essential component of the high solids paint compositions ofthis invention is an amine-aldehyde crosslinking agent. Amine-aldehydecrosslinking agents suitable for crosslinking hydroxy functional bearingmaterials are well known in the art. Typically, these crosslinkingmaterials are products of reactions of melamine, or urea withformaldehyde and various alcohols containing up to and including 4carbon atoms. Preferably, the amine-aldehyde crosslinking agents usefulin this invention are condensation products of formaldehyde withmelamine, substituted melamine, urea, benzoguanamine or substitutedbenzoguanamine. Preferred members of this class are methylatedmelamine-formaldehyde resins such as hexamethoxymethylmelamine. Theseliquid crosslinking agents have substantially 100 percent nonvolatilecontent as measured by the foil method at 45° C. for 45 minutes. For thepurposes of the invention it should be recognized that it is importantnot to introduce extraneous diluents that would lower the final solidscontent of the coating.

Particularly preferred crosslinking agents are the amino crosslinkingagents sold by American Cyanamid under the trademark "Cymel". Inparticular, Cymel 301, Cymel 303 and Cymel 1156, which are alkylatedmelamine-formaldehyde resins, are useful in the compositions of thisinvention.

The amine-aldehyde materials function as a cross-linking agent in thecomposition of the invention by reacting with hydroxy functionalitypresent in the composition (i) as an organic hydroxyl group on thehydroxy functional organophosphate ester, (ii) as a hydroxyl group onthe optional hydroxy functional additive including any excess diol ortriol from the organophosphate synthesis, or (iii) as a result ofesterification of the pendant epoxy functionality on the epoxyfunctional copolymer.

In order to achieve the outstanding properties which make these coatingcompositions particularly useful as automotive topcoat materials, it isessential that the amount of amino crosslinking agent be sufficient tosubstantially completely crosslink the hydroxy functionality in thecoating composition. Therefore, the amino crosslinking agent should beincluded in the composition in an amount sufficient to provide at leastabout 0.4 equivalents, preferably between about 0.6 and about 2.1equivalents, of nitrogen crosslinking functionality for each equivalentof hydroxy functionality included in the composition.

OPTIONAL HYDROXY FUNCTIONAL ADDITIVE

Additional hydroxy functionality other than that achieved byesterification of pendant epoxy functionality of the epoxy functionalcopolymer or by the hydroxy functional organophosphate ester may beachieved by adding a hydroxy functional additive in amounts up to about45 weight percent based on the total of the three above discussedcomponents and the hydroxy functional additive itself. Such a materialserves to provide additional hydroxy functionality so as to provide amore intimate crosslinked structure in the final cured product. Thehydroxy functional additives useful in the composition are preferablyselected from various polyols having a number average molecular weight(M_(n)) of between about 150 and about 6,000, preferably between about400 and about 2500. As used herein the term polyol means a compoundhaving two or more hydroxyl groups.

The polyols useful for the invention preferably are selected from thegroup consisting of: (i) hydroxy functional polyesters; (ii) hydroxyfunctional polyethers; (iii) hydroxy functional oligoesters, (iv)monomeric polyols, (v) hydroxy functional copolymers produced by freeradical polymerization of monoethylenically unsaturated monomers, one ofwhich bears hydroxy functionality and which is included in the copolymerin an amount ranging from about 2.5 to about 30 weight percent of thecopolymer and (vi) mixtures of (i)-(v).

The hydroxy functional polyesters useful in the invention are preferablyfully saturated products prepared from aliphatic dibasic acidscontaining 2-20 carbon atoms, such as succinic acid, glutaric acid,adipic acid, azelaic acid, etc., and short chain glycols of up to andincluding 21 carbon atoms, such as ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol,1,4-butylene glycol, neopentyl glycol 1,4-cyclohexane dimethylol,1,6-hexamethylene glycol and 2-ethyl-2-methyl-1,3-propane diol. Themolecular weight of these materials ranges from about 200 to about 2500and the hydroxyl number ranges from about 30 to about 230. The hydroxylnumber is defined as the number of milligrams of potassium hydroxideneeded for each gram of sample to neutralize the acetic acid generatedduring the reaction between the polyol and excess acetic anhydride. Thepolyester polyols utilized in the invention are low melting, soft waxysolids which are easily maintained in the molten state.

Among preferred polyesters are products derived from the esterificationof ethylene glycol and 1,4 butane diol with adipic acid, ethylene glycoland 1,2 propylene glycol with adipic acid, azelaic acid and sebacic acidcopolyester diols, and mixtures thereof.

Among useful polyether diols are polytetramethylene ether glycol,polyethylene glycol, polypropylene glycol and the like.

The hydroxy functional oligoesters useful as hydroxy functionaladditives in the compositions of the invention are oligoesterspreferably having a molecular weight of between about 150 and about3000. Such oligoesters may be selected from the group consisting of: (i)oligoesters prepared by reacting a dicarboxylic acid with a monoepoxidesuch as an alkylene oxide; (ii) oligoesters prepared by reacting apolyepoxide with a monocarboxylic acid; and (iii) oligoesters preparedby reacting a hydroxy functional monocarboxylic acid with either a mono-or polyepoxide.

The oligoester prepared by reacting a dicarboxylic acid with an alkyleneoxide is a low molecular weight adduct which has a narrow molecularweight distribution when compared to similar compositions made by normalpolyester manufacturing techniques. The adduct is prepared by reacting adibasic carboxylic acid with alkylene oxides, preferably ethylene oxideor propylene oxide, in the presence of a catalyst. Preferreddicarboxylic acids are C₆ -C₁₂ aliphatic acids such as adipic acid,,azelaic acid sebacic acid or dodecane dicarboxylic acid. Mixtures ofthese acids or mixtures of the aliphatic dicarboxylic acids witharomatic dicarboxylic acids also yield suitable hydroxy functionaloligoesters.

The preparation of oligoesters from monocarboxylic acids andpolyepoxides is well known and is described, for example, in U.S. Pat.Nos. 2,456,408 and 2,653,141. Numerous hydroxy functional oligoesterswithin this general category will be apparent to those skilled in theart.

The third type of hydroxy functional oligoester, i.e., those prepared byreaction of a hydroxy functional monocarboxylic acid with an epoxide isdescribed in U.S. Pat. No. 3,404,018. While the epoxides employed inaccordance with the teachings of that patent are polyepoxides,oligoesters may be prepared in a similar manner to that describedtherein by employing a monoepoxide, such as an alkylene oxide, and ahydroxy functional monocarboxylic acid as described therein. Numerousmonoepoxide materials suitable for this purpose will be apparent tothose skilled in the art.

Among the numerous monomeric polyols which may be employed as thehydroxy functional additive are the various short chain glycols of up toand including 21 carbon atoms which are useful in preparing the hydroxyfunctional polyesters discussed above. Other conventional polyhydricalcohols such as glycerols and sugar alcohols are also among thenumerous monomeric polyols which will be apparent to those skilled inthe art.

The hydroxy bearing copolymer useful as the hydroxy functional additivemay be formed from monoethylenically unsaturated monomers, with betweenabout 10 and about 30 weight percent bearing hydroxyl functionality.

The long list of hydroxy functional monomers which may be employed inthese hydroxy functional copolymers includes, but is not limited to, thefollowing esters of acrylic or methacrylic acid and aliphatic alcohols:2-hydroxyethyl acrylate; 3-chloro-2-hydroxypropyl acrylate;2-hydroxy-1-methylethyl acrylate; 2-hydroxypropyl acrylate;3-hydroxy-propyl acrylate; 2,3 dihydroxypropyl acrylate; 2-hydroxy-butylacrylate; 4-hydroxybutyl acrylate; diethyleneglycol acrylate;5-hydroxypentyl acrylate; 6-hydroxyhexyl acrylate; triethyleneglycolacrylate; 7-hydroxyheptyl acrylate; 2-hydroxymethyl methacrylate;3-chloro-2-hydroxypropyl methacrylate; 2-hydroxy-1-methylethylmethacrylate; 2-hydroxypropyl methacrylate; 3-hydroxypropylmethacrylate; 2,3 dihydroxypropyl methacrylate; 2-hydroxybutylmethacrylate; 4-hydroxybutyl methacrylate; 3,4 dihydroxybutylmethacrylate; 5-hydroxypentyl methacrylate; 6-hydroxyhexyl methacrylate;1,3-dimethyl-3-hydroxybutyl methacrylate; 5,6 dihydroxyhexylmethacrylate; and 7-hydroxyheptyl methacrylate.

Although one of ordinary skill in the art will recognize the manydifferent hydroxy bearing monomers including those listed above could beemployed, the preferred hydroxy functional monomers for use in thehydroxy functional resin of the invention are C₅ -C₇ hydroxy alkylacrylates and/or C₅ -C₇ hydroxy alkyl methacrylates, i.e., esters of C₂-C₃ dihydric alcohols and acrylic or methacrylic acids.

The remainder of the monomers forming the hydroxy functional copolymer,i.e., between about 90 and about 70 weight percent, are othermonoethylenically unsaturated monomers. These monoethylenicallyunsaturated monomers, as was the case with respect to the epoxyfunctional copolymer discussed above, are preferably alpha-betaolefinically unsaturated monomers. As was also the case with respect tothe epoxy functional copolymer, the preferred alpha-beta olefinicallyunsaturated monomers are acrylates and preferably are employed in excessof 50 weight percent of the total copolymer. Preferred acrylate monomersare esters of C₁ -C₁₂ monohydric alcohols and acrylic or methacrylicacids. Monovinyl hydrocarbons and other modifying monomers may also beemployed in the same proportion as they are employed in the epoxyfunctional copolymer discussed above.

OTHER MATERIALS

In addition to the above discussed components, other materials may beincluded in the high solids coating compositions of the invention. Theseinclude materials such as catalysts, antioxidants, U.V. absorbers,solvents, surface modifiers and wetting agents as well as pigments. Thesolvents used in the coating compositions of the invention are thosewhich are commonly used. Typical solvents useful in the coatingcompositions facilitate spray application at high solids content andinclude toluene, xylene, methyethyl ketone, acetone, 2-ethoxy-1-ethanol,2-butoxy-1-ethanol, diacetone alcohol. tetrahydrofuran, ethylacetate,dimethylsuccinate, dimethylglutarate, dimethyladipate or mixturesthereof. The solvent in which the epoxy functional copolymer of thecoating composition is prepared, may be employed as the solvent for thecoating composition thus eliminating the need for drying the epoxyfunctional copolymer after preparation if such is desired. As mentionedabove, the nonvolatile solids content of the high solids coatingcomposition is at least 60 percent and preferably 70 percent or more,thus limiting the amount of solvent included in the composition.

Surface modifiers or wetting agents are common additives for liquidpaint compositions. The exact mode of operation of these surfacemodifiers is not known, but it is thought that their presencecontributes to better adhesion of the coating composition to the surfacebeing coated and helps formation of thin coating on surfaces,particularly metal surfaces. These surface modifiers are exemplified byacrylic polymers containing 0.1-10 percent by weight of a copolymerizedmonoethylenically unsaturated carboxylic acids such as methacrylic acid,acrylic acid or itaconic acid, cellulose acetate butyrate, silicon oilsor mixtures thereof. Of course, the choice of surface modifier orwetting agent is dependent upon the type of surface to be coated andselection of the same is clearly within the skill of the artisan.

The high solids coating composition of the invention also may includepigments. As noted above, the high solids compositions of this inventionare particularly useful when the coating composition includes metallicflake as a pigment. The rapid set and curing of the compositioneliminates problems associated with redistribution of the metallic flakein the composition. The amount of pigment in the high solids coatingcomposition may vary, but preferably is between about 3 and about 45weight percent based on the total weight of the paint composition. Ifthe pigment is metallic flake, the amount ranges from about 1 to about 7weight percent.

APPLICATION TECHNIQUES

The high solids coating composition can be applied by conventionalmethods known to those in the art. These methods include roller coating,spray coating, dipping or brushing and, of course, the particularapplication technique chosen will depend on the particular substrate tobe coated and the environment in which the coating operation is to takeplace.

A particularly preferred technique for applying the high solids coatingcompositions, particularly when applying the same to automobiles astopcoats, is spray coating through the nozzle of a spray gun.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" is intended tomean parts by weight.

EXAMPLE 1

(a) Five Hundred (500) grams of dry (dried over molecular sieves)2-ethyl-1,3 hexane diol are placed in a three-necked round bottom flaskequipped with a stirrer, dropping funnel and a thermometer. Solidphosphorus pentoxide is added portionwise with continuous stirring andan exothermic reaction occurs. The addition of phosphorus pentoxide isregulated to maintain the temperature at 50° C. and test portions of thereaction mixture are withdrawn at short intervals of time and titratedwith potassium hydroxide solution. The addition of P₂ O₅ is continueduntil the acid equivalent weight equals 500. The reaction mixture isstirred at 50° C. for one more hour and is filtered. The acid equivalentweight, by titration with KOH solution, is found to be 485.

(b) In a round-bottom four-necked flask, equipped with a stirrer, adropping funnel, a thermometer and a condenser, 500 ml of methyl amylketone is brought to reflux under nitrogen. The following mixture ofmonomers is employed for polymer synthesis:

    ______________________________________                                                       Weight/grams                                                                              Wt. %                                              ______________________________________                                        Butyl methacrylate                                                                             127.5         17                                             Ethylhexyl acrylate                                                                            180           24                                             Glycidyl methacrylate                                                                          195           26                                             Methyl methacrylate                                                                            210           28                                             Styrene          37.5           5                                             ______________________________________                                    

Thirty-seven (37) grams of tert-butyl perbenzoate is added to the abovemonomers and the resulting solution added dropwise to refluxing methylamyl ketone over a period of one hour and ten minutes. The heating andstirring is continued for half an hour after the addition is completeand then two more grams t-butyl perbenzoate are added portionwise. Thereaction mixture is refluxed for two more hours and then allowed to coolto room temperature. The molecular weight of the copolymer is determinedby Gel Permeation Chromatography and found to be M_(n) =3250 andMw/M_(n) =2.2. The calculated Tg of the polymer is 9° C. and thesolution viscosity (#4 Ford cup) is 41 seconds.

Eighty (80) parts of the copolymer solution prepared in (b) and 40 partsof Cymel 301 are dissolved in 20 parts of butyl acetate and 44.5 partsof the hydroxy phosphate prepared in (a) are added to this solution. Theresulting formulation is spray applied to steel test panels and thepanels are baked at 130° C. for 20 minutes to obtain a glossy (81/20°)coating with excellent hardness, adhesion and solvent (xylene and methylamyl ketone) resistance. The coating does not show any loss of gloss oradhesion after 14 days exposure in the Cleveland Humidity Chamber.

EXAMPLE 2

Five (5) parts of aluminum flakes (65% in naphtha) are mixed well with80 parts of the copolymer solution from Example 1(b). Thirty-nine (39)parts Cymel 301 and 30 parts of butyl acetate are added to the abovemixture and the resulting material is filtered through a coarsefiltering cloth. Forty-five (45) parts of hydroxy phosphate from Example1(a) are added to the filtrate and the resulting formulation sprayapplied to primed steel test panels in a three coat application. Theintermediate flash time is one minute and the final flash is fiveminutes. The panels are baked at 115° C. for 20 minutes to obtain asilver metallic coating with excellent hardness, adhesion and solvent(xylene and methyl amyl ketone) resistance.

EXAMPLE 3

(a) The hydroxyphosphate preparation described in Example 1(a) isrepeated with an increased amount of phosphorus pentoxide to obtain anacid equivalent weight of 271.

(b) Fifty (50) parts of the polymer solution from Example 1(b) is mixedwith 24 parts of hexamethoxymethyl melamine, 5 parts of polypropyleneglycol (Pluracol P710, BASF Wyndotte Co.) and 15 parts of butyl acetate.14.9 parts of hydroxyphosphate from (a) is added to the above solutionand the resulting formulation is spray applied to steel test panels. Thepanels are baked at 130° C. for 20 minutes to obtain glossy (85/20°)coatings with excellent hardness, adhesion and solvent (xylene andmethtyl ethyl ketone) resistance. The coating does not show any loss ofgloss or adhesion after 14 days exposure in a Cleveland HumidityChamber.

EXAMPLE 4

Six (6) parts of aluminum flakes (65% in naphtha) are mixed well with 70parts of the polymer solution from Example 1(b). Thirty-nine (39) partsCymel 301 and 30 parts of butyl acetate are added to the above mixtureand the resulting material is filtered through a coarse filtering cloth.Twenty-five (25) parts of hydroxy phosphate from Example 3(a) are addedto the filtrate and the resulting formulation spray applied to primedsteel test panels in a three coat application; the intermediate flashtime in one minute and the final flash five minutes. The panels arebaked at 115° C. for 20 minutes to obtain silver metallic coatings withexcellent hardness, adhesion and solvent (xylene and methyl ethylketone) resistance.

EXAMPLE 5

The following monomers are utilized in the synthesis of a glycidylmethacrylate polymer.

    ______________________________________                                                         Wt. g.   Wt. %                                               ______________________________________                                        Butyl methacrylate 120        16                                              Ethylhexyl acrylate                                                                              142.5      19                                              Glycidyl methacrylate                                                                            195        26                                              Methyl methacrylate                                                                              255        34                                              Styrene            37.5        5                                              ______________________________________                                    

The polymerization is carried out as outlined in Example 1 by employing500 grams of methyl amyl ketone and 30 grams of tert-butyl perbenzoate.The addition of initiator and the monomer mixture is complete in twohours and the reaction mixture refluxed for one additional hour. Twograms of initiator are then added and the reaction mixture refluxed fortwo hours. The molecular weight determined by Gel PermeationChromatography is found to be M_(n) =3168 and Mw/M_(n) =2.15. The Tg ofthis polymer is calculated to be 20° C.

Thirty-two (32) parts of the above polymer solution, fourteen (14) partsof hexamethoxymethyl melamine (Cymel 301) and two parts of1,4-Cyclohexanedimethanol are dissolved in ten parts of butyl acetate.9.9 parts of hydroxyphosphate from Example 3(a) are added to the abovesolution and the resulting formulation spray applied to primed steelpanels; the panels are baked at 120° C. for 20 minutes to obtain acoating with excellent physical properties.

EXAMPLE 6

Twenty-seven (27) parts of the polymer described in Example 5, 16 partsof Cymel 301 and 5 parts of Acryloid OL-42 (Rohm and Haas Chem. Co.) aredissolved in 10 parts of butyl acetate. 8.4 parts of hydroxyphosphatefrom Example 3(a) is added to the above solution and the resultingformulation drawn on a steel test panel and baked at 130° C. for tenminutes to obtain a glossy coating with excellent hardness, adhesion andsolvent resistance.

EXAMPLE 7

(a) One hundred (100) grams of 1,4-cyclohexanemethanol are dissolved in80 grams of butyl acetate at 50° C. and the procedure outlined inExample 1(a) is followed to obtain a hydroxyphosphate with an acidequivalent weight of 645.

(b) Eighty (80) parts of the polymer solution prepared in Example (b),10 parts of bis-(hydroxypropyl) azelate (product of propylene oxide andazelaic acid) and 45 parts of ethoxy methoxymethylbenzoguanamine (Cymel1123, American Cyanamid) are dissolved in 25 parts of butyl acetate and58.2 parts of hydroxyphosphate from (a) are added to this solution. Theresulting formulation is spray applied to primed steel panels and bakedat 130° C. for 20 minutes to obtain hard, glossy coatings with excellentadhesion and solvent resistance.

EXAMPLE 8

Thirty-five (35) parts of the polymer solution prepared in Example 5, 17parts of hexamethoxymethyl melamine (Cymel 301, American Cyanamid) and 5parts of caprolactone based hydroxyester PCPO300 (Union Carbide) aredissolved in 10 parts of butyl acetate. 10.7 parts of hydroxyphosphatefrom Example 3(a) are added to the above solution and the resultingformulation spray applied to primed steel test panels. The panels arebaked at 130° C. for 20 minutes to obtain coatings with excellenthardness, adhesion, gloss and solvent resistance (xylene and methylethyl ketone).

EXAMPLE 9

The following mixture of monomers is used in the polymer synthesis:

    ______________________________________                                                              Wt. %                                                   ______________________________________                                        Butyl Methacrylate      25                                                    Glycidyl acrylate       30                                                    Methyl methacrylate     40                                                    Styrene                  5                                                    ______________________________________                                    

The polymerization is carried out as outlined in Example 1 to obtain a50% solution of the polymer.

Seventy (70) parts of the above polymer solution, 15 parts ofbis-(hydroxypropyl) azelate (reaction product of propylene oxide andazelaic acid) and 35 parts of hexamethoxymethyl melamine (Cymel 301) aredissolved in 10 parts of butyl acetate. 22.3 parts of hydroxyphosphatefrom Example 3(a), are added to the above solution and the resultingformulation spray applied to primed steel panels. The panels are bakedat 130° C. for 15 minutes to obtain glossy (88°/20°) coatings withexcellent adhesion, hardness and solvent (xylene and methyl ethylketone) resistance.

EXAMPLE 10

(A) A hydroxy acrylic copolymer is prepared from the following monomers:

    ______________________________________                                                       Wt. grams Wt. %                                                ______________________________________                                        Butyl methacrylate                                                                             1000        50                                               Hydroxyethyl acrylate                                                                          400         20                                               Methyl methacrylate                                                                            400         20                                               Styrene          200         10                                               ______________________________________                                    

One hundred (100) grams tert-butyl perbenzoate is added to the abovemonomer mixture and the resulting solution added dropwise over a periodof two hours to 1400 grams of refluxing methyl amyl ketone undernitrogen. The heating and stirring is continued for half an hour afterthe addition is complete and then five grams of tert-butyl perbenzoateare added portionwise to the reaction mixture. The reaction mixture isrefluxed for an additional ninety (90) minutes and then allowed to coolto room temperature. The molecular weight is determined by GelPermeation Chromatography M_(n) -2540 and Ms/M_(n) =1.94

(B) A solution of 1250 grams of 2-ethyl-1,3 hexane diol in 1250 grams ofbutyl acetate is placed under nitrogen in a three-necked round bottomflask equipped with a mechanical stirrer. Phosphorus pentoxide (442grams) is added portionwise with continuous stirring, an exotherimicreaction occurs and the addition of P₂ O₅ is regulated to maintain thetemperature between about 50° and about 60° C. After completing theaddition (about 4 hours), the reaction mixture is stirred for three morehours. The acid equivalent weight, by titration with KoH solution, isfound to be 315.

Forty (40) parts of the polymer from (A), 45 parts by weight of theglycidyl methacrylate polymer from Example 1(b) and 34 parts ofhexamethoxymethyl melamine (Cymel 301) are dissolved in 20 parts ofbutyl acetate. 16.3 parts of hydroxyphosphate from (b) is added to theabove solution and the resulting formulation spray applied to primedsteel test panels. The panels are baked at 130° C. for 20 minutes toobtain glossy coatings with excellent hardness, adhesion and solvent(xylene and methyl ethyl ketone) resistance.

EXAMPLE 11

Twenty-five (25) parts of polymer from Example 5, 25 parts of thehydroxypolymer from Example 10 and 27 parts of hexabutoxymethyl melamine(Cymel 1156) are dissolved in 15 parts of butyl acetate. 9.1 parts ofhydroxyphosphate from 10(b) is added to the above solution and theresulting formulation spray applied to primed steel panels. The panelsare baked at 130° C. for 20 minutes to obtain glossy coatings withexcellent hardness, adhesion and solvent resistance.

EXAMPLE 12

(a) Fifty (50) grams of 1,4-benzenedimethanol are dissolved in 150 gramsof 2-ethyl-1,3-hexanediol and 40 ml of butyl acetate. Phosphoruspentoxide is added portionwise to the above solution as described inExample 1(a) to obtain a hydroxyphosphate with an acid equivalent weightweight of 364.

(a) Thirty (30) parts of glycidyl methacrylate polymer from Example 5. 5parts of bis-(hydroxypropyl) azelate and 18 parts of ethoxymethoxymethylbenzoguanamine (Cymel 1123, American Cyanamid) are dissolved in 10 partsof butyl acetate. 13.2 parts of the hydroxyphosphate are added to theabove solution and the resulting formulation spray applied to primedsteel panels. The panels are baked at 180° C. for 20 minutes to obtainhard, glossy coatings with excellent adhesion and solvent (xylene andmethyl ethyl ketone) resistance.

EXAMPLE 13

(a) Example 1(a) is repeated to obtain a hydroxy phosphate with acidequivalent weight of 212.

(b) Twenty-five (25) parts of glycidyl methacrylate polymer from Example1, 20 parts of hydroxy polymer from Example 10, 5 parts ofbis(hydroxypropyl) azelate and 19 parts of butoxymethyl glycoluril(Cymel 1170, American Cyanamid) are dissolved in 15 parts of butylacetate. 5.8 parts of the hydroxyphosphate are added to the abovesolution and the resulting formulation spray applied to primed steelpanels. The panels are baked at 130° C. for 20 minutes to obtain hard,glossy coatings with excellent adhesion and solvent (xylene and methylethyl ketone) resistance.

EXAMPLE 14

Thirty (30) parts of glycidyl methacrylate polymer from Example 5, 7parts of Acryloid OL42 (Rohm and Haas Chem. Co.) and 27 parts ofbutoxymethyl urea resin (Beetle 80, American Cyanamid) are dissolved in20 parts of butyl acetate. 7.3 parts of hydroxyphosphate from Example13(a) are added to the above solution and the resulting formulationspray applied to primed steel panels. The panels are baked at 130° C.for 20 minutes to obtain a hard and glossy coating.

EXAMPLE 15

The following mixture of monomers is employed in the synthesis of apolymer:

    ______________________________________                                                              Wt. %                                                   ______________________________________                                        Allyl glycidyl ether    30                                                    Butyl methacrylate      25                                                    Methyl methacrylate     30                                                    Styrene                 15                                                    ______________________________________                                    

The polymerization is carried out as outlined in Example 1 to obtain a52% solution of the polymer in methyl amyl ketone.

Thirty-one (31) parts of the above polymer, 20 parts of the hydroxypolymer from Example 8, 17 parts of hexamethoxymethyl melamine (Cymel301, American Cyanamid) are dissolved in 10 parts butyl acetate. 8.9parts of hydroxyphosphate from Example 13(a) are added to the abovesolution and the resulting formulation spray applied to primed steelpanels. The panels are baked at 130° C. for 20 minutes to obtain hard,glossy coatings with excellent adhesion and solvent (xylene and methylethyl ketone) resistance.

EXAMPLE 16

The following monomers are employed in the synthesis of this polymer.

    ______________________________________                                                              Wt. %                                                   ______________________________________                                        Butyl methacrylate      40                                                    Glycidyl methacrylate   15                                                    Methyl methacrylate     40                                                    Styrene                  5                                                    ______________________________________                                    

The polymerization is carried out in methyl amyl ketone by employing1.8% (by wt. of the monomers) of the initiator. The molecular weightfrom Gel Permeation Chromatography is found to be M_(n) =5750, Mw/M_(n)=24. The solids content is found to be 54% by weight.

Sixty (60) parts of this polymer solution, 70 parts of the polymer fromExample 5 and 50 parts of hexamethoxymethyl melamine (Cymel 301) aredissolved in 30 parts of butyl acetate. 15.4 parts of hydroxyphosphatefrom Example 3(a) is added to the above solution and the resultingformulation spray applied to primed steel panels. The panels are bakedat 130° C. for 20 minutes to obtain coatings with excellent hardness andadhesion and solvent (xylene and methyl ethyl ketone) resistance.

EXAMPLE 17

Three hundred Fifty (350) grams of titanium dioxide are mixed with 350parts of Acryloid OL-42 (Rohm and Haas Chem. Co.) and 25 parts of butylacetate. The above mixture is taken up in a porcelain bottle containingporcelain beeds and is put on a roller mill for 16 hours. Forty (40parts of the above millbase are mixed with 28 parts of polymer fromExample 1, 5 parts of hycroxy ester Desmophen KL5-2330 (Rohm and HaasChem. Co.), 13 parts of hexamethoxymethyl melamine (Cymel 301) and 20parts of butyl acetate. 6.7 parts of hydroxyphosphate from Example 13are added to the above mixture and the resulting formulation sprayapplied to primed steel panels. The panels are baked at 120° C. for 20minutes to obtain coatings with excellent physical properties.

EXAMPLE 18

Five hundred (500) parts of titanium dioxide and 250 parts of Ferriteyellow are mixed with 500 parts of Acryloid OL-42 (Rohm and Haas Chem.Co.), 7.8 parts of dispersing agent BYK P104S (Mellinckrodt) and 200parts of butyl acetate. The millbase is prepared as described in Example17.

Thirty-five parts of this millbase are mixed with 50 parts of polymerfrom Example 5, 25 parts of hexamethoxymethyl melamine, 3 parts of1,4-cyclohexanedimethanol and 22 parts of butyl acetate. 17.9 parts ofhydroxyphosphate from Example 10(b) are added to the above mixture andthe resulting formulation spray applied to primed steel panels. Thepanels are baked at 115° C. for 20 minutes to obtain coatings withexcellent physical properties.

EXAMPLE 19

Fifty (50) parts of blue pigment Phthalo Blue are mixed with 500 partsof Acryloid OL-42 (Rohm and Haas Chem. C9.) and 44 parts of butylacetate, the millbase was ground as described in Example 17.

Twenty-five (25) parts of the above millbase are mixed with 6 parts ofaluminum flakes (65% in naphtha), 41 parts ofbis-(hydroxypropyl)azelate, 29 parts of hexamethoxymethyl melamine(Cymel 301) and 20 parts butyl acetate. 9.8 parts of thehydroxyphosphate from Example 13 is added to the above mixture and theresulting formulation spray applied to primed steel panels in four coatswith one minute flash time between coats. After five minutes final flashthe panels are baked at 130° C. for 20 minutes to obtain a blue metalliccoating with excellent hardness, adhesion and solvent resistance.

EXAMPLE 20

Ninety-eight (98) grams of phosphoric acid and 50 ml of butyl acetateare placed in a round-bottom flask fitted with a condenser and adropping funnel and cooled with an ice water mixture. Propylene oxide,136 grams, is added dropwise with continuous stirring; the addition iscomplete in two hours.

Example 1 is repeated by substituting 21 parts of the abovehydroxyphosphate for the hydroxyphosphate used therein. The coatingshave excellent physical properties.

EXAMPLE 21

The blue metallic formulation described in Example 19 is repeated byemploying 10.2 parts of the hydroxyphosphate described in Example 20.The formulation is spray applied to primed steel panels in three coatswith one minute final flash the panels are baked at 100° C. for 20minutes to obtain blue metallic coatings with excellent hardness,adhesion and solvent resistance.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchmodifications which fall within the true scope of this invention beincluded within the terms of the appended claims.

I claim:
 1. A thermosetting coating composition adapted for lowtemperature bake applications which contains greater than about 60% byweight of nonvolatile solids, and which, exclusive of pigments, solventsand other nonreactive components, consists essentially of:(A) acopolymer bearing pendant epoxy functionality, having a number averagemolecular weight (M_(n)) of between about 1500 and about 10,000 and aglass transition temperature (Tg) of between about -25° C. and about 70°C., said copolymer consisting of between about 10 and about 30 weightpercent of monoethylenically unsaturated monomers bearing glycidylfunctionality and between about 90 and about 70 weight percent of othermonoethylenically unsaturated monomers; (B) a reactive catalystcomprising at least one hydroxy functional organophosphate ester havingthe formula: ##STR3## wherein n=1 to 2 and R is selected from the groupconsisting of mono- or dihydroxy alkyl, cycloalkyl, or aryl radicals;(C) an amine-aldehyde crosslinking agent; and (D) up to 45 weightpercent based on the total weight of (A), (B), (C), and (D) of a hydroxyfunctional additive having a number average molecular weight (M_(n)) ofbetween 150 and about 6000, said hydroxy functional organophosphateester being included in said composition in an amount sufficient toprovide between about 0.67 and about 1.4 equivalents of acidfunctionality for each equivalent of pendant epoxy functionality on saidcopolymer, and said amine-aldehyde crosslinking agent being included insaid composition in an amount sufficient to provide at least about 0.4equivalents of nitrogen crosslinking functionality for each equivalentof hydroxy functionality included in said composition either as (i) anorganic hydroxyl group on said organophosphate ester, (ii) a hydroxylgroup on said hydroxy functional additive, or (iii) as a result ofesterification of said pendant epoxy functionality of said copolymerduring cure of said coating composition.
 2. A composition in accordancewith claim 1, wherein said monoethylenically unsaturated monomersbearing glycidyl functionality are selected from glycidyl esters andglycidyl ethers.
 3. A composition in accordance with claim 2, whereinsaid monoethylenically unsaturated monomers bearing glycidylfunctionality are selected from glycidyl esters of monoethylenicallyunsaturated carboxylic acids.
 4. A composition in accordance with claim1, wherein said other monoethylenically unsaturated monomers in saidcopolymer are selected from the group consisting of acrylates and othermonoethylenically unsaturated vinyl monomers.
 5. A composition inaccordance with claim 4, wherein said acrylate monomers comprise atleast about 50 weight percent of the total monomers in said copolymerand are selected from esters of C₁ -C₁₂ monohydric alcohols and acrylicor methacrylic acids.
 6. A composition in accordance with claim 1,wherein said hydroxy functional organophosphate esters are esterswherein R is a mono- or dihydroxy alkyl, cycloalkyl or aryl radicalcontaining 3 to 10 carbon atoms.
 7. A composition in accordance withclaim 1, wherein at least a portion of said organophosphate esters areesters wherein R is a mono- or dihydroxy alkyl radical containing 3 to10 carbon atoms.
 8. A composition in accordance with claim 1, whereinsaid organophosphate ester is a monoester.
 9. A composition inaccordance with claim 1, wherein said organophosphate ester is adiester.
 10. A composition in accordance with claim 1, wherein saidorganophosphate ester is a mixture of mono- and diesters.
 11. Acomposition in accordance with claim 10, wherein said hydroxy functionalorganophosphate esters are esters wherein R is a mono- or dihydroxyalkyl, cycloalkyl or aryl radical containing 3 to 10 carbon atoms.
 12. Acomposition in accordance with claim 10, wherein at least a portion ofsaid organophosphate esters are esters wherein R is a mono- or dihydroxyalkyl radical containing 3 to 10 carbon atoms.
 13. A composition inaccordance with claim 1 wherein said reactive catalyst including saidhydroxy functional organophosphate ester is the reaction product of anexcess of an alkyl, cycloalkyl or aryl diol or triol and phosphoruspentoxide.
 14. A composition in accordance with claim 1 wherein saidreactive catalyst including said hydroxy functional organophosphateester is the reaction product of an excess of an alkyl, cycloalkyl oraryl triol in which at least one of the hydroxyl groups is secondary,and phosphorus pentoxide.
 15. A composition in accordance with claim 1wherein said reactive catalyst including said hydroxy functionalorganophosphate ester is the reaction product of an alkyl, cycloalkyl oraryl monoepoxide and phosphoric acid in a molar ratio of between about1:1 and about 2:1.
 16. A composition in accordance with claim 15 whereinsaid monoepoxide also bears hydroxy functionality.
 17. A composition inaccordance with claim 15 wherein said monoepoxide is selected frommonoepoxy esters, monoepoxy ethers and alkylene oxides.
 18. Acomposition in accordance with claim 1, wherein said amino resincrosslinking agent is amine-aldehyde selected from the group consistingof condensation products of formaldehyde with melamine, substitutedmelamine, urea, benzoguanamine and substituted benzoguanamine, andmixtures of said condensation products and is included in an amountsufficient to provide between about 0.6 and about 2.1 equivalents ofnitrogen crosslinking functionality per equivalent of hydroxyfunctionality.
 19. A composition in accordance with claim 1, whereinsaid hydroxy functional additive is a polyol selected from the groupconsisting of (i) hydroxy functional polyesters, (ii) hydroxy functionalpolyethers, (iii) hydroxy functional oligoesters, (iv) monomericpolyols, (v) hydroxy functional copolymers formed from monoethylenicallyunsaturated monomers, one or more of which bears hydroxy functionalityand which is included in said copolymer in amounts ranging from about 10to about 30 weight percent of said copolymer, and (vi) mixtures of(i)-(v).
 20. A composition in accordance with claim 1, wherein saidorganophosphate ester is included in said composition in an amountsufficient to provide between about 1.2 equivalents of acidfunctionality for each equivalent of pendant epoxy functionality on saidcopolymer.